Attention-spreading Based on Hierarchical Spatial Representations for Connected Objects

Abstract

Abstract& Attention selects objects or groups as the most fundamental unit, and this may be achieved through a process in which attention automatically spreads throughout their entire region. Previously, we found that a lateralized potential relative to an attended hemifield at occipito-temporal electrode sites reflects attentionspreading in response to connected bilateral stimuli [Kasai, T., & Kondo, M. Electrophysiological correlates of attention-spreading in visual grouping. NeuroReport, 18, 93-98, 2007]. The present study examined the nature of object representations by manipulating the extent of grouping through connectedness, while controlling the symmetrical structure of bilateral stimuli. The electrophysiological results of two experiments consistently indicated that attention was guided twice in association with perceptual grouping in the early phase (N1, 150-200 msec poststimulus) and with the unity of an object in the later phase (N2pc, 310/330-390 msec). This suggests that there are two processes in objectbased spatial selection, and these are discussed with regard to their cognitive mechanisms and object representations. &

Are objects the same as groups? ERP correlates of spatial attentional guidance by irrelevant feature similarity

“…By controlling the symmetrical structure of bilateral stimuli, Kasai (2010) found that the typical P1 attention effect (150-210 ms post-stimulus onset) was obtained, regardless of the connectedness of the bilateral stimuli, but, importantly, the subsequent N1 attention effect (150-200 ms) and N2 (310/330-390 ms) showed decreases in amplitudes in the connected conditions. Note that previous studies with the bilateral-stimulus paradigm have not reported the N1 attention itself, perhaps due to a confounding of grouping factors.…”

“…Note that previous studies with the bilateral-stimulus paradigm have not reported the N1 attention itself, perhaps due to a confounding of grouping factors. The results of Kasai (2010) suggested that, since connectedness was irrelevant to the task, spatial attention was obligatorily spread or guided to the opposite side of the object region to the task-relevant side. Furthermore, the specific stimulus manipulations (unconnected, weakly-connected, and strongly-connected conditions) led to the following interpretation: N1 is associated with the extent of perceptual grouping because the attention effect diminished as connectedness increased, and N2 is associated with the unity of an object because the attention effect diminished for connected objects regardless of the degree of connectedness.…”

“…Using a sustained focal attention task that involved bilateral stimulus arrays (Heinze et al, 1990(Heinze et al, , 1994Woldorff et al, 2002), we previously examined object/group-based spatial attention for connected objects (Kasai, 2010;Kasai & Kondo, 2007). By controlling the symmetrical structure of bilateral stimuli, Kasai (2010) found that the typical P1 attention effect (150-210 ms post-stimulus onset) was obtained, regardless of the connectedness of the bilateral stimuli, but, importantly, the subsequent N1 attention effect (150-200 ms) and N2 (310/330-390 ms) showed decreases in amplitudes in the connected conditions.…”

“…Using the same experimental paradigm as in the previous study for connected objects (Kasai, 2010), the present study tested the case of grouping according to similarity in achromatic color or contrast polarity (one lighter and one darker than a grey background), or in simple geometric shapes (see Figure 1). Three stimulus conditions were tested: similar Group-based attention 6 condition, dissimilar-color condition, and dissimilar-shape condition.…”

“…Stimuli with different widths (thin and thick) were selected for the left and right sides to make an asymmetric figure, since symmetry is also a grouping factor (e.g., Saiki, 2000) and may cause a ceiling effect (Kasai, 2010;Kasai & Kondo, 2007). All combinations of widths, colors, and shapes were presented in equal probability so that estimates of attention and grouping effects are collapsed across physical differences, i.e., different similarity conditions involved the same stimuli at particular locations, but the similarity relations between bilateral stimuli differed.…”